Technical Field
This invention relates to heat fixing mechanisms in electrostatographic copiers and printers, and more particularly to a long life, heat efficient, and low cost fuser roller thereof having powder metal gudgeons.
In electrostatographic reproduction apparatus such as copiers and printers, it is well known, as disclosed in U.S. Pat. Nos. 4,229,950 and 4,536,076, to use a heat and pressure fixing mechanism including a heated roller for fusing a toner image onto a suitable receiver. The heated roller which may be heated internally or externally, may consist of an external coating and an inner core made of a high thermally conductive metallic material such as aluminum. Typically, the heated roller is supported to the frame of the copier or printer on a pair of gudgeons or end caps, and is rotatably driven, for example, by a motor connected to one of the gudgeons.
Ordinarily, in order to achieve excellent and cost effective fixing results, relatively high fusing pressures are required, and the heated roller must be repeatedly heated and maintained at a high and precise fusing temperature in the range of about 300.degree.-400.degree. F., for example. The supporting end caps or gudgeons therefore must be able to repeatedly withstand substantial forces at such a high temperature in order to produce the required fixing pressures. Additionally, for precisely controlling the fusing temperature heat loss (from the roller through the gudgeons to the surrounding environment) must be effectively minimized.
Conventionally, materials such as plastics, which have a relatively low thermal conductivity, have been used to construct gudgeons for such heated roller. Unfortunately, however, because such plastic materials do not have physical characteristics, for example, of strength, stiffness and rate of thermal expansion, that match those of the aluminum core of such a heated roller, the connection between such core and the gudgeon typically has involved the use of fastening means. The connection as such is therefore usually difficult to make as well as difficult to maintain. The undesirable result is early failure of the connection due to loosening or fracture of the fastening means. Over time, plastic gudgeons additionally tend to degrade under the high temperatures and pressures required for electrostatographic image fixing. On the otherhand, metallic gudgeons in general are unacceptable because of the relatively high thermal conductivity of metals.
However, because of the relatively low metallic thermal conductivity of powder metal materials, the use of powder metal materials such as powder metal stainless steel for constructing such gudgeons, has been suggested, for example, in U.S. Pat. No. 4,536,076. Unfortunately however, the thermal conductivity, even of a powder metal stainless steel gudgeon, can vary significantly depending on controllable parameters such as the density and the interconnected porosity of such gudgeon. More importantly, as suggested in Japanese kokai No. J57158867-A, the durability, and hence the life and cost, for example, of a heat fixing roller (including such a gudgeon) depends significantly on the manner and the stability of the connection between such gudgeon and the core of such roller.